Alan Gaffney says it is 'a huge shame' to lose star man Courtney Lawes for the rest of the season.
Lawes suffered a knee ligament injury during England's Six Nations defeat at France last Saturday and will now require surgery.
The 29-year-old will need a 14-week rehabilitation period, meaning he will miss Saints' final five Aviva Premiership matches.
Lawes has been one of the stand-out players at Franklin's Gardens this season, having also impressed for the British & Irish Lions last summer.
He has made 15 appearances during this campaign, but he will now face a lengthy recovery period as he bids to get fit for next season.
"This is of course a huge shame for Courtney, who has had another exceptional season so far," said technical coaching consultant Gaffney.
"But he is in great hands here at Franklin's Gardens, and we know he will be diligent with his rehab and come back fighting fit as soon as is possible."